iTunes is multi-window -- double-click any playlist to see. Even if it weren't, you don't want it to quit when you close its last window, you want the music to

iTunes is multi-window -- double-click any playlist to see. Even if it weren't, you don't want it to quit when you close its last window, you want the music to play on. The distinction is arbitrary, though. There are plenty of single-window apps I'd like to stay running.